Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $220.49   6.493%   $234.8064   $234.81   $234.80   $234.80  
  Purchase #2 $163.40   3.374%   $168.9131   $168.91   $168.90   $168.90  
  Purchase #3 $115.39   6.274%   $122.6296   $122.63   $122.65   $122.60  
  Purchase #4 $55.85   6.738%   $59.6132   $59.61   $59.60   $59.60  
  Purchase #5 $224.77   7.648%   $241.9604   $241.96   $241.95   $242.00  
  Purchase #6 $142.38   3.315%   $147.0999   $147.10   $147.10   $147.10  
  Purchase #7 $55.51   6.658%   $59.2059   $59.21   $59.20   $59.20  
  7 purchase totals = $977.79       $1,034.2285   $1,034.23   $1,034.20   $1,034.20